Abstract: Provided are a novel screening method for a substance that potentiates damaged DNA repair capability, based on a test with DNA repair as an index with improved sensitivity as a simplified version of the currently available unscheduled DNA synthesis (UDS) assay based on 3H-thymidine and BrdU or recovery of RNA synthesis (RRS) test, and the like. By measuring UDS activity quickly at high sensitivity using a method of nucleotide fluorescence detection with the use of a click chemistry reaction (e.g., detection of terminal alkyne-modified nucleoside by means of a reporter molecule containing an azide moiety), a substance capable of DNA repair can be selected.